The soybean, Glycine max (L.) Merril, is a major economic crop worldwide and is a primary source of vegetable oil and protein (Sinclair and Backman, Compendium of Soybean Diseases, 3rd Ed. APS Press, St. Paul, Minn., p. 106. (1989)). The growing demand for low cholesterol and high fiber diets has also increased importance of soybean as a health food.
Soybean varieties grown in the United States have a narrow genetic base. Six introductions, ‘Mandarin,’ ‘Manchu,’ ‘Mandarin’ (Ottawa), “Richland,” ‘AK’ (Harrow), and ‘Mukden,’ contributed nearly 70% of the germplasm represented in 136 cultivar releases. The genetic base of cultivated soybean could be widened through the use of exotic species. In addition, exotic species may possess such key traits as disease and stress resistance. At present, the traits of many exotic species are inaccessible in part due to limitations with crossing soybean plants from extremely different maturity groups. Most soybean variety development crosses are made between parents within 10 maturity days of each other. If the parents differ greatly in maturity, the progeny plants segregate widely for maturity. In order for breeders to obtain and select for soybean plants of the desired maturity group, they must produce and maintain a large number of progeny plants, the practice of which is cost prohibitive.
Plant maturity and yield are closely associated in soybean. An increase of one day in maturity may be equivalent to a ˜0.7 bu/A increase in yield. Conversely, a decrease in maturity is often penalized with a ˜0.7 bu/A decrease in yield. The correlation of plant maturity and yield confounds the evaluation of potential quantitative trail loci (QTLs) and candidate genes associated with yield. The ability to genetically fix maturity within a soybean plant would be helpful and assist in elucidating traits associated with yield.
Soybean plants are short day plants, therefore flowering is initiated by short days due to a decrease in photoperiod (Garner & Allard, J. Agric. Res. 18, 553-606 (1920)). Consequently, photoperiod (day length) and temperature response of the soybean plant determine areas of plant adaptation. Due to photoperiod sensitivity, soybean genotypes are often grown in narrow zones of latitude to optimize yield. Northern soybean varieties, in contrast to Southern varieties, initiate flowering with longer days. Northern varieties planted south of their adaptation zone exhibit accelerated flowering, limited plant growth and reduced yield. Southern soybean varieties planted north of their adaptation zone will have delayed flowering with a potential for frost damage that may reduce yield.
Soybean plant varieties are classified based on bands of adaptation that are determined by latitude and day length. In North America, soybeans are categorized into 13 maturity groups with the designations ranging from maturity groups 000, 00, 0, and I through X. The earliest maturity group 000 soybeans are adapted to the north (45° latitude), while the latest maturity group X soybeans are adapted to regions near the equator. Soybean plants in maturity groups 000 to IV have indeterminate plant structure, while soybean plants in maturity groups V through X have determinate plant structure. Determinate varieties cease vegetative growth after the main stem terminates in a cluster of mature pods. Indeterminate varieties develop leaves and flowers simultaneously throughout a portion of their reproductive period, with one to three pods at the terminal apex. Early maturity varieties (000 to III) are adapted to northern latitudes with the maturity designation increasing in southern latitudes. The maturity group is determined by the maturity date. Plants are considered mature when 95% of the pods have reached their mature color. The maturity date is typically described as a measurement of days after August 31st in the northern hemisphere.
There is a need in the art of plant breeding to identify genomic regions associated with the maturity group of a soybean plant. At present, soybean breeders are limited to crossing plants within similar maturity groups. In addition, a number of traits, like oil levels, are influenced by latitude and maturity growing region. Therefore, there is a need for a rapid, cost-efficient method to pre-select for maturity group of soybean plants. The present invention includes a method for screening and selecting a soybean plant for a preferred plant maturity using single nucleotide polymorphism (SNP) technology.